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The extraction of microamounts of REE(III), U(VI), and Th(IV) from HClO4 solutions with solutions of 2,6-bis(diphenylphosphorylmethyl) pyridine N-oxide (I) in 1,2-dichloroethane was studied depending on the HClO4 concentration in the equilibrium aqueous phase. The stoichiometry of the extracted complexes was determined. It was shown that compound I extracts REE(III), U(VI), and Th(IV) from dilute HClO4 solutions with much higher efficiency than from HNO3 solutions. With an increase in the concentration of acids, the magnitude of the “perchlorate” effect upon extraction of REE(III) and U(VI) decreases, and Th(IV) is extracted by compound I from HClO4 solutions with lower efficiency than from HNO3 solutions.

The extraction of microamounts of U(VI), Th(IV), and REE(III) from HNO3 solutions in the form of complexes with 2,6-bis(diphenylphosphorylmethyl)pyridine N-oxide (I) was studied in relation to the kind of organic diluent and to the HNO3 concentration in the equilibrium aqueous phase. The stoichiometry of the extractable complexes was determined. With respect to the ability to extract Th(IV) and REE(III), compound I considerably surpasses tetraphenylmethylenediphosphine dioxide and tetraalkyl-substituted analogs of I.

Physicochemical principles of preparation of U(VI) carbonate solutions in the step of oxidative dissolution of U3O8 and UO2 in the Carbex process are considered. Carbonate solutions with the U(VI) concentration higher than 100 g L–1, suitable for subsequent final purification of uranium by extraction, can be prepared under the conditions of formation of U(VI) carbonate–peroxide complexes in the course of dissolution with prevention of hydrolysis of U(VI) compounds. The behavior of impurities simulating some fission products in the course of oxidative dissolution was studied, and the decontamination factors of U(VI) from the chosen simulated fission products were determined.

Interaction of UO2, U3O8, ZrO2, Nb2O5, CeO2, Ce2O3, Pr6O11, Eu2O3, Yb2O3, Tb7O12, and Re metal with lithium, sodium, and potassium carbonates in the temperature interval 300–900°С was studied using methods of thermal analysis and X-ray diffraction. The major products of the high-temperature reactions are alkali metal uranates and diuranates, and in the case of ZrO2, Nb2O5, and lanthanide oxides, oxides of metals in higher oxidation states and salts of the corresponding metal-containing acids, formed by reactions of the oxides with sodium carbonate.

A series of impregnated sorbents based on di-tert-butyldicyclohexyl-18-crown-6 (DTBDCH18C6), various diluents (1-octanol, nitrobenzene, telomeric alcohol n3), and supports (Porolas-Т, LPS-500, hydrophobized silica gel) for removing tracer and weighable amounts of Sr ions from nitric acid solutions were prepared. The distribution coefficient of tracer amounts of 90Sr on all the synthesized sorbents increases with an increase in the HNO3 concentration in the range 1–7 M. The most pronounced increase in the sorption occurs with an increase in the HNO3 concentration to 3 M. The maximal distribution coefficient of 90Sr (Kd = 158 cm3 g–1) is reached for the sorbent based on DTBDCH18C6 and 1-octanol in 7 M HNO3. Experiments on sorption of weighable amounts of Sr2+ ions show that the static capacity of all the prepared sorbents for Sr in nitric acid solutions amounts to 4.3, 9.2, and 8.4 mg g–1 for the sorbents based on 1-octanol, nitrobenzene, and telomeric alcohol n3, respectively. The synthesized sorbents are suitable for radioanalytical determination of Sr radionuclides in liquid radioactive waste and in radioactively contaminated natural objects.

The results of the development of a medical-purpose extraction 188Re generator and of 188Re radiopharmaceuticals are presented. The main advantage of this generator is the possibility of using as starting material tungsten oxide of natural isotope composition, irradiated in a reactor with medium neutron flux [(1.0–1.4) × 1014n cm–2 s–1]. Separation of the parent 188W and daughter 188Re was performed in a centrifugal semicounter-current contactor developed at the Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences. The 188Re yield is about 90%, and the radiochemical purity (Na188ReO4 content) is ≥95%. The content of the 188W impurity is less than 1 × 10–3% relative to the 188Re activity, and the content of other radionuclides is less than 1 × 10–4%. The resulting Na188ReO4 solution was registered as “Active pharmaceutical substance” and was used in the development and subsequent preclinical trials of several radiopharmaceuticals for radionuclide therapy of pain syndrome accompanying the development of cancer metastases into the skeleton, and also for radiosynovectomy.

A series of phosphoryl podands of acid type, differing in the length of the polyether chain and structure of the terminal group, were synthesized. The compounds obtained were tested as complexing components of impregnation-type sorbents. The regular trends of the Mo sorption from model solutions of ammonium molybdate in HNO3 in relation to the qualitative and quantitative composition of the sorbents were studied by extraction chromatography. The composition of a new impregnation-type complexing sorbent for selective recovery of Mo from nitric acid solutions was developed and optimized, and conditions were determined for its practical use. The sorbent allows efficient recovery of 99Mo and its separation from products of reprocessing of irradiated uranium materials in process solutions of the Mayak Production Association. The sorbent also allows separation of 99Mo and 99m Tc, which makes it potentially suitable for use in 99Mo/99m Tc generators of chromatographic type.

The extraction of microamounts of REEs(III), U(VI), and Th(IV) from HNO3 solutions with solutions of acidic phosphoryl-containing podands in 1,2-dichloroethane was studied. The stoichiometry of the extractable complexes was determined. The influence of the extractant structure and aqueous phase composition on the efficiency and selectivity of the recovery of REEs(III), U(VI), and Th(IV) into the organic phase was considered.

The Th content in commercially available Nd2O3 samples with the main substance content of 99.0–99.998% was found to be 2–8, and that of U, 3–230 ppb. Therefore, to obtain Nd meeting the requirements of the experiment on studying neutrinoless double β-decay, it should be purified to reduce the content of Th and U impurities by a factor of 103–104. To this end, the extraction of Nd, Th, and U from hydrochloric acid media with solutions of trioctylphosphine oxide (TOPO) in toluene was studied. The distribution ratios of Th increase with a decrease in the HCl concentration in the initial aqueous solution. With an increase in the Cl− concentration in the aqueous phase, the U distribution ratios decrease, probably because of a decrease in the concentration of the free extractant due to the extraction of Nd and HCl. On the contrary, the distribution ratios of Th increase with an increase in the Cl− concentration in the aqueous phase, with the slope of the straight line in the coordinates logDTh-log[Cl−]aq close to 7, which may be due to coextraction of Th with Nd in the form of the complex ThNdCl7. The enthalpies of formation of the extractable complexes of Th and U were determined from the temperature dependence of the extraction of Nd, Th, and U chlorides with a 0.1 M solution of TOPO in toluene. The optimal extraction system was chosen for Nd purification to remove traces of Th and U: organic phase, 0.1 M solution of TOPO in toluene; aqueous phase, 2.4 M NdCl3 + 0.1 M HCl. From the initial aqueous solution contaning 574 ppt Th and 2837 ppt U, by single extraction with an equal volume of 0.1 M TOPO in toluene, an aqueous solution containing

Extraction of REE with solutions of neutral organophosphorus compounds (TBP, TIAP, DIOMP) in a new diluent, linear alkylbenzene (LAB), was studied. LAB exhibits significant advantages over known diluents: high flash point (+147°C), nontoxicity, absence of odor, low cost, availability, and good compatibility with polymeric structural materials. LAB is well compatible with TBP, TIAP, and DIOMP. Extraction of HNO3 and REE nitrates is not accompanied by precipitation of extractable complexes or by formation of a second organic phase in a wide concentration range, up to saturation of the extractant. The major extractable complex in extraction of REE nitrates is Ln(NO3)3·3NOPC, where NOPC = TBP, TIAP. The main parameters of extraction systems (distribution ratios, separation factors) with LAB are similar to those of the related systems with paraffin hydrocarbons as diluents. Experiments on group separation of REEs on a 56-step extraction installation gave results agreeing with the calculation data.

Complexes of Gd with carboxylic acids C4–C9 were prepared, and their properties were studied: solubility in water and organic solvents in relation to temperature, melting points, and decomposition points. A procedure was developed for removing water from gadolinium 2-methylvalerate Gd(2MVA)3 to a final content not exceeding 0.01%. To increase the solubility of Gd(2MVA)3 in low-polarity organic solvents and to stabilize the resulting organic solutions, it was suggested to add extractants such as 2-methylvaleric acid (H2MVA) or neutral organophosphorus compounds: triisoamylphosphine oxide (TIAPO) or trioctylphosphine oxide (TOPO). Liquid Gd-loaded organic scintillators based on Gd(2MVA)3 solutions with additions of H2MVA, TIAPO, and TOPO in trimethylbenzene (TMB), phenylxylylethane (PXE), and their mixtures with dodecane were prepared. Long-term tests (up to 2 years) of the stability of the optical properties of the scintillators obtained proved their stability at temperatures of up to 30°C. At elevated temperatures (40°C and higher), the scintillators degrade. The previously made suggestion that water in the scintillator negatively affects its optical properties in prolonged storage was confirm

Diphosphorylated dibenzo crown ethers with 4,4′(5′)-bis[n-butyl(hydroxy)]phosphoryl substituents at the benzene rings of dibenzo-18-crown-6 (I), dibenzo-21-crown-7 (II), and dibenzo-24-crown-8 (III) were prepared and studied with the aim of developing new highly effective and selective extractants for recovery and separation of metals. Extraction of a solution containing Al, B, Ba, Bi, Ca, Cd, Co, Cr, Cu, Fe, Ga, Ge, In, K, La, Li, Mg, Mn, Mo, Na, Ni, Pb, Re, Sc, Sr, Tl, V, Y, and Zn (10 ppm each) and an Am(III) solution in 0.01–5 M HNO3 with 0.05 M solutions of the endoreceptors in chloroform was studied. For endoreceptor III, the maximal distribution ratios of metals Dmmax are ranked in the following order: Sc (>103) > Am (162) > Mo (129) > V (75.9) > In (29.3) > Bi (16.5) > Fe (4.7) > Rb (1.0) > Pb (0.34) > Ga (0.18) > Ge (0.11) > Al, B, Ba, Ca, Cd, Co, Cr, Cu, K, La, Li, Mg, Mn, Na, Ni, Re, Sr, Tl, V, Zn (

Extraction properties of lariat crown ethers were studied. Dibenzo-substituted crown ethers of a new class, with electron-donor side phosphoryl groups -P(O)R2 (R = iso-C3H7O, n-C4H9O, C6H5), were proposed as extracting agents. The oxygen atoms of the phosphoryl groups form additional bonds with metal ions in the extractable complexes. Extraction of 31 metals from 0.01–7 M HNO3 with five diphosphorylated derivatives of 18-crown-6 and 21-crown-7 was studied. Diphosphorylated endoreceptors were prepared by introduction of organophosphorus fragments into the structure of dibenzo crown ethers. The extraction properties of these compounds depend on the electron-donor properties of the phosphoryl oxygen. If the sum of the reaction constants of the substituents at the phosphorus atom of these groups is −1.77 or more negative, the phosphoryl oxygen is coordinated with the metal of the extracted metal salts and the endoreceptos are effective and selective extracting agents for the following metals (the maximal distribution ratio is given): Tl (1.1) ≈ Rb (1.1) 103). In this case, the extraction ability of diphosphorylated dibenzo crown ether increases by a factor of 102–103 as compared to that of the unsubstituted analogs. The resulting compounds can be used as endoreceptors of new generation with unique extraction properties.

Extraction of In with solutions of 2-methylvaleric acid (H2MVA) in trimethylbenzene (TMB) was studied. Depending on pH of the equilibrium aqueous phase, the extracted indium species are In(2MVA)3 · 3(H2MVA), In(2MVA)3, [In(2MVA)x(OH)3−x]n, etc., where 2MVA is the 2-methylvalerate anion and n is the degree of polymerization. By the extraction method, In-containing liquid organic scintillators (LOSs) with the following parameters were obtained: [In] = 50–96 g l−1, transparency 2–3 m, light output 68% relative to TMB. Long-term precision trials of the scintillators in the Gran Sasso underground laboratory (Italy) confirmed that the scintillator parameters were stable and met the requirements of the LENS experiment. A procedure was developed for preparing solid anhydrous indium hydroxycarboxylates, and their properties were studied. LOSs based on solutions of solid indium hydroxycarboxylates in TMB were prepared and subjected to long-term trials in which the transparency and light output were monitored. One of the major factors responsible for the instability of indium-containing LOSs is the presence of water in the organic phase.

Extraction of rare-earth elements (REEs) and Am(III) from acid solutions with alkyl-substituted crown ethers dibenzo-and dicyclohexano-18-crown-7 in the chloroform-water system was studied. Dicyclo-hexano-18-crown-6 and its alkyl derivatives extract REEs and Am(III) in the presence of trichloroacetic acid (HTCA) considerably better, compared to dibenzo-18-crown-6 and its alkyl derivatives and to the systems containing HNO3 and HC1O4 instead of HTCA. The distribution ratios of the cerium-group REEs are considerably higher than those of the yttrium-group REEs. In all the cases, the metal to crown ether ratio in theextractable complexes is 1:1.

A comparison was made of the properties of solvents meeting the requirements posed on Gd-loaded organic liquid scintillators (transparency, light output, compatibility with the structural materials of the detector). The optical properties of the solvents were examined in relation to various factors (purity of the initial reagents, concentrations of Gd and scintillation additives). Extraction of Gd with C4 C8 carboxylic acids was examined. The composition of the extractable Gd complexes with 2-methylvaleric and 2-ethylhexanoic acids, GdR3·3HR·mH2O (where m = 1–2, depending on the solvents used), was determined. The solubility of water in 2-ethylhexanoic and 2-methylvaleric acids was examined. Scintillators based on Gd 2-methylvalerates have better parameters than those based on the other carboxylic acids tested. The instability of the optical properties of the Gd carboxylate solutions is presumably due to the presence of water in the scintillator. Possible methods of water removal from the organic phase were discussed.

The extraction of uranium and of transuranium and rare-earth elements from nitric acid solutions with solutions of 4,4′(5′)-bis(dialkylphosphoryl)-,-bis(diphenylphosphoryl)-, and-bis[(O-alkyl)phosphoryl]-benzo-n-crown-m ethers (n = 18, m = 6; n = 21, m = 7; n = 24, m = 8) in 1,2-dichloroethane and chloroform was studied. The distribution ratios of U(VI), Pu(IV), Am(III), and Eu(III) in the extraction depend both on the experimental conditions and on the structural features of the ligands. In the range [HNO3] = 0.02–1.0 M, the metal distribution ratios DM depend on the mutual steric orientation of the phosphoryl groups. With the cis (4,4′) isomers, DM is higher than with the trans (4,5′) isomers and with the isomer mixtures. With the compound containing the (n-BuO)2P(O) groups in the cis position as example, it was found that the highest distribution ratios DU = 0.98 were observed in 3 M HNO3; DPu = 5.1, in 0.5 M HNO3; and DAm = 0.007, at pH 2. For the trans conformer under the same conditions, DM of U(VI), Pu(IV), and Am(III) is 0.091, 1.8, and 0.003, respectively. The macroring size (number of carbon atoms n), under other conditions equal, also significantly affect the extraction activity of the reagent. With the extraction of Am(III) from 0.01–3 M HNO3 as example, it was shown that the crown ethers with n = 21 are the most efficient with all the substituents. The maximum of DAm shifts toward higher HNO3 concentrations with increasing n. The coordinating power of phosphoryl-containing ligands based on functionally substituted benzo-21-crown-7 ether in the extraction of Am(III) from 0.01–3 M HNO3 decreases in the order (n-BuO)(OH)P(O)-≫ (n-BuO)2P(O)-> Ph2P(O)-, under other conditions equal. The extraction ability of di(n-BuO)(OH)P(O)-dibenzo-21-crown-7 (DAm = 814 in extraction from 0.1 M HNO3) exceeds that of the other compounds studied by more than two orders of magnitude. Conditions were found for the selective extractive separation of Am(III) and Eu(III) using bis[(O-alkyl)(OH)phosphoryl]dibenzo-21-crown-7, with a separation factor of >90 at [HNO3] = 0.01 M.

Aiming to find extractants suitable for recovery of cesium from nitric acid solutions with a high sodium content, two types of alkylated derivatives of 18-crown-6 were studied. Derivatives of the first type (five compounds) were prepared by introducing alkyl substituents into the macroring. Derivatives of the second type were prepared by introducing alkyl substituents into phenyl or cyclohexyl fragments of dibenzo-18-crown-6 (DB18C6) and dicyclohexyl-18-crown-6 (DCH18C6) (16 compounds). The alkylated crown ethers exhibit different reactivity depending on the substitution mode. Introduction of two alkyl substituents into the phenyl rings of dibenzo-18-crown-6 allowed preparation of compounds ensuring the Cs/Na separation factor as high as 100 and more.

Extraction of metals from 0.1–7 M HNO3 with 0.05 M chloroform solutions of functionalized crown ethers containing (n-C4H9O)2P(O)- fragments and differing in the polyether ring size (18-crown-6, 21-crown-7, 24-crown-8) was studied. An increase in the size of the macroring in diphosphorylated dibenzo crown ethers leads to an appreciable increase in the performance of the extractants toward a number of metals, due to participation of phosphoryl groups in the complexation. At the same time, the reactivity of the macroring varies insignificantly, which decreases the selectivity of the recovery of metals forming host-guest complexes. These features should be taken into account when designing new macrocyclic extractants of the lariat type.